Three metabolic activation systems, intrasanguinous-host mediated assay, isolated perfused organs, and in vitro microsomes are being compared in their effectiveness for detecting chemical mutagens. Dimethylnitrosamine (DMN) was used as the test mutagen and strain SV3 of Salmonella, which detects forward mutations in the arabinose operon, is used as the tester microorganism. CD1 male mice and CD male rats are used for mammalian activation.